This invention relates to semiconductor wafer manufacture, and in particular to the step of polishing the wafer surface for planarization. The method of the invention is particularly applicable to wafers containing copper circuitry.
During the fabrication of semiconductor wafers, it is common practice to polish the wafer surface at certain points in the process in order to maintain a planar surface. Maintaining such a surface is important because of the very fine detailed circuitry created on the wafer surface, in layers atop each other, and the requirements of the precision instruments used to create the layered circuitry.
In the past, the predominant, if not exclusive, metal used as the conductive component of semiconductors was aluminum. In more recent years, techniques have been developed to use copper, which offers the advantage of better electrical conductivity and the potential for significantly improved performance in several devices using semiconductors, particularly those utilizing a battery pack power supply that must be periodically recharged.
The newer copper technology has, however, presented additional challenges in the fabrication process. One of these relates to the fouling of polishing pads used to planarize the semiconductor wafer surfaces. While pads ordinarily must be conditioned periodically, even when aluminum is the conductive metal on the wafer, much more frequent reconditioning is required when copper is used. It has been found that polishing with standard chemical polishing aids produces a dark residue (xe2x80x9cdebrisxe2x80x9d) that fouls pad surfaces, requiring more frequent pad conditioning, and ultimately more frequent pad replacement. More frequent pad conditioning reduces productivity, and more frequent pad replacement increases operating expenses. Therefore, there is a clear incentive to find ways to reduce the frequency of pad conditioning and pad replacement.
The invention provides a method of conditioning polishing pads used in the polishing of semiconductor wafers that comprise copper circuitry. The method includes treating the polishing surface of the pad with a treating solution that includes a reactant for copper debris formed on the pad. This treatment removes substantially all the copper debris, and is followed by a rinsing step, that in turn removes the treating solution so that the pad is free of reactants that might damage the next set of wafers to be polished.
In preferred embodiments, the reactant for copper debris is an acid, and more particularly a carboxylic acid such as oxalic acid, citric acid, malonic acid, succinic acid, lactic acid, and the like. Other acids able to react with copper residue are also useful. In accordance with the invention, it is also preferred to at least partially neutralize the acid to reduce the pH to the range from about 1.0 to about 6.0.
After cleaning the polishing pad with the treatment solution, the pad may be rinsed with standard pad conditioning solutions, and/or deionized water until the surface is substantially free of the treatment solution and suitable for reuse in the polishing of semiconductor wafers.